This invention relates in general to the use of magnetic pulse welding techniques to secure two metallic components together, such as a yoke and a driveshaft tube in a vehicular driveshaft assembly. In particular, this invention relates to an improved method for performing such a magnetic pulse welding operation that protects the inductor from potential damage that can result from the performance of this operation.
In most land vehicles in use today, a drive train system is provided for transmitting rotational power from an output shaft of an engine/transmission assembly to an input shaft of an axle assembly so as to rotatably drive one or more wheels of the vehicle. To accomplish this, a typical vehicular drive train assembly includes a hollow cylindrical driveshaft tube having first and second end fittings (such as tube yokes) secured to the opposed ends thereof. The first end fitting forms a portion of a first universal joint, which provides a rotatable driving connection from the output shaft of the engine/transmission assembly to the driveshaft tube while accommodating a limited amount of angular misalignment between the rotational axes of these two shafts. Similarly, the second end fitting forms a portion of a second universal joint, which provides a rotatable driving connection from the driveshaft tube to the input shaft of the axle assembly while accommodating a limited amount of angular misalignment between the rotational axes of these two shafts.
In vehicular driveshaft assemblies of this general type, it is usually necessary to permanently secure the first and second end fittings to the ends of the driveshaft tube. Traditionally, conventional welding techniques have been used to permanently join the first and second end fittings to the ends of the driveshaft tube. As is well known, conventional welding techniques involve the application of heat to localized areas of two metallic members, which results in a coalescence of the two metallic members. Such conventional welding techniques may or may not be performed with the application of pressure, and may or may not include the use of a filler metal. Although conventional welding techniques have functioned satisfactorily in the past, there are some drawbacks to the use thereof in joining the first and second end fittings to the ends of the driveshaft tube. First, as noted above, conventional welding techniques involve the application of heat to localized areas of the two metallic members. This application of heat can cause undesirable distortions and weaknesses to be introduced into the metallic components. Second, while conventional welding techniques are well suited for joining components that are formed from similar metallic materials, it has been found to be somewhat more difficult to adapt them for use in joining components formed from dissimilar metallic materials. Third, conventional welding techniques are not easily adapted for joining components that have different gauge thicknesses. Inasmuch as the production of vehicular driveshaft assemblies is usually a high volume process, it would be desirable to provide an improved method for permanently joining these metallic components together in a manner that avoids the drawbacks of conventional welding techniques.
Magnetic pulse welding is an alternative process that has been proposed to secure the first and second end fittings to the opposed ends of the driveshaft tube. To accomplish this, a hollow driveshaft tube having an end portion and an end fitting having a neck portion are initially provided. The end portion of the driveshaft tube can be hollow to allow the neck portion of the end fitting to be disposed co-axially therein. Alternatively, the neck portion of the end fitting can be hollow to allow the end portion of the driveshaft tube to be disposed telescopically therein. If desired, one of the adjacent surfaces of the neck portion of the end fitting or the end portion of the driveshaft tube can be tapered at least slightly relative to the other. Regardless, an annular gap is provided between the end portion of the driveshaft tube and the neck portion of the end fitting. Then, an electrical inductor is provided concentrically about or within the co-axially overlapping portions of the driveshaft tube and the end fitting. The inductor is energized to generate a magnetic field that either collapses the outer member inwardly into engagement with the inner member or expands the inner member outwardly into engagement with the outer member. In either event, the high velocity impact of the two members, as well as the large pressure exerted thereon, cause them to become permanently joined together. When one of the adjacent surfaces is tapered, the energization of the inductor causes the two members to collide one another in an axially progressive manner from one end of the tapered surface to the other. This slanting type of collision is one of the physical conditions that is usually necessary to achieve a strong, high-quality weld in the process of magnetic pulse welding.
As mentioned above, prior to being joined together, the two components are initially spaced apart from one another such that an annular gap exists between the adjacent surfaces thereof. This gap typically filled with air. Also, the adjacent surfaces of the two components are usually covered with oxide films or other contaminants. To achieve a strong weld between the two components using magnetic pulse welding (or, for that matter, any other type of cold welding process), it is important to remove these films and contaminants from the adjacent surfaces of the two components.
When the inductor is energized to form the pulsed magnetic field, the high velocity movement between the two components rapidly closes the annular gap, causing the air that was initially present in the gap to be quickly expelled outwardly therefrom. In the area where the surfaces collide with high velocity at a tapered angle, a circular cumulative flow of air is created. Fortunately, during this expulsion of the air from the annular gap, a very effective cleaning process occurs automatically as a result of the slanting collision of the adjacent surfaces of the two components to be welded. Specifically, the circular cumulative flow of air functions to remove the oxide films and other contaminants from the adjacent surfaces of the two components functions to clean such surfaces directly before the welding process occurs, which is the best type of cleaning.
This cumulative flow of air and contaminants possesses a large amount of energy and supersonic velocity. For example, it creates a loud sound like thunder if the flow is allowed to escape to the atmosphere. If the cumulative flow is reflected from an obstacle, such as a shoulder formed on the end fitting or one or more surfaces of tooling for performing the magnetic pulse welding operation, it can be directed toward the inductor that generated the magnetic field. In this instance, the insulation and other elements of the inductor can be contaminated and otherwise adversely affected in a short number of welding cycles. For example, insulation provided on the inductor can degrade significantly fast if the air and other portions of the cumulative flow are captured inside a closed space, the volume of which decreases fast. This situation is typical when, for example, the yoke shoulder is used as a stop to facilitate pre-assembly of the parts to be welded inside the inductor. In this case, a very powerful secondary flow is created as a result of a gas breakdown at the end of the collision of the welded parts through a very narrow circular gap between the shoulder and the end of the tube. Similar to the cumulative flow, this secondary flow is circular, has high velocity, and has high temperature. Unlike the cumulative flow, which is directed axially, the secondary flow is directed radially, i.e., perpendicular to the inductor insulation. The secondary flow is highly concentrated in an axial direction and acts as a sharp circular razor. The secondary flow can literally cut the inductor insulation within several welding cycles. Obviously, this is unacceptable in a manufacturing process because breakdown of the inductor is possible.
In order to prevent this from occurring, it has been suggested to provide a nonmetallic, annular shield between the axially overlapping portions of the two components and the inductor during the magnetic pulse welding process. The high velocity secondary flow created during the magnetic pulse welding operation impinges upon the shield, thus protecting the inductor therefrom premature. However, the use of such a shield has been found to be relatively time-consuming and, therefore, relatively inefficient, particularly in the context of the high volume production process associated with the manufacture of vehicular driveshaft assemblies. Thus, it would be desirable to provide an improved method for performing a magnetic pulse welding operation that reduces or eliminates the possibility of the cumulative flow escaping, as well as the possibility of forming a secondary flow in the direction of the inductor, thereby protecting the inductor from the potential wear and damage that breakdown can result therefrom.